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Studies on bruising in broiler chicken carcases

Griffiths, Geoffrey Lyn (1987) Studies on bruising in broiler chicken carcases. PhD thesis, Murdoch University.

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Investigations were undertaken to determine the importance of downgrading to the Australian broiler chicken processing industry. Particular emphasis was placed on the causes of bruising.

Daily downgrading of broiler carcasses in individual processing plants varied from 7 to 27% of the total production with bruising the most common cause of carcass rejection. Based on information received from 4 processing plants the average number of carcasses downgraded daily due to farm damage, bruising, and plant damage was 2.07%, 5.83% and 3.65% The respectively. annual cost of downgrading was estimated to be in the order of $A11.9 million, while the losses due to bruising and "red skin" carcasses were estimated to be $5.7 million and $1.1 million respectively.

The role of processing plant procedures in causing bruising was investigated. It was found that bruises of any consequence could not be induced after chickens were stunned. Australian processing methods were surveyed and it was concluded that some broilers were not killed by the neck cutting device. Other chickens were unintentionally electrocuted, prior to exsanguination. Some chickens were still technically alive when they entered the scald tank and as a result formed red skin carcasses, in which the skin is red due to vascular congestion and superficial bruising of carcasses.

It was found that slaughter technique did not adversely affect the carcass appearance, or the amount of blood retained in the edible tissues, as long as the chickens were bled out prior to entering the electrical stunning devices should be adjusted to result in electrocution of all broilers.

In this study it was found that physical injury was responsible for the bruises observed and there were no factors predisposing the broilers to bruising. Twenty per cent of the drumstick bruises were associated with tibial fractures, while 94% of thigh bruises occurred as a result of epiphyseal fractures, femoral neck fractures or dislocations. The depth of bruising varied according to the site affected. All of the bruises on the medial aspect of the thigh and 96% of drumstick bruises involved the skin, subcutis and underlying muscle. However 90% of the breast bruises and most of the wing bruises were superficial and did not extend into the muscle.

The histological response to injury of skin and muscle was studied in experimental birds. It was found that an orderly sequence of inflammation and repair occurred in bruised muscle. Acid phosphatase was demonstrated to be present in high concentrations in inflammatory cells and this was utilised as a histo-chemical "marker" to demonstrate an early inflammatory response. Histological criteria were established to enable a distinction to be made between bruises that were 0-2 hours old, from those that were either 2-12 hours, or a number of days old. Based on the examination of 108 bruised drumstick portions it was found that 25% of bruises occurred prior to catching, while 40% were inflicted at the time of catching and crating and 30% occurred after the broilers arrived at the processing plant. Eight-three per cent of thigh bruises and 90% of wing bruises occurred less than 8 hours prior to slaughter.

It was only possible to complete this study with the full co-operation and generous support of the Australian chicken meat industry. It is the only one of its kind undertaken in Australia, and much of the information has now been extended to the industry.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Nairn, Malcolm and Purcell, D.A.
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